The present invention relates to stretch fabrics. In one aspect, the invention relates to stretch fabrics comprising synthetic and natural fibers while in another aspect, the invention relates to such fabrics comprising crosslinked, heat-resistant elastic fibers capable of withstanding dyeing and heat-setting processes. The crosslinked, heat-resistant elastic fibers are useful in various durable or repeated-use fabric applications such as, but not limited to, clothing, undergarments, sports apparel and upholstery. The crosslinked, heat-resistant elastic fibers can be conveniently formed into fabrics using well-known techniques such as, for example, by using co-knitting techniques with cotton, nylon, and/or polyester fibers.
A material is typically characterized as elastic if it has a high percent elastic recovery (that is, a low percent permanent set) after application of a biasing force. Ideally, elastic materials are characterized by a combination of three important properties, i.e., (i) a low percent permanent set, (ii) a low stress or load at strain, and (iii) a low percent stress or load relaxation. In other words, there should be (i) a low stress or load requirement to stretch the material, (ii) no or low relaxing of the stress or unloading once the material is stretched, and (iii) complete or high recovery to original dimensions after the stretching, biasing or straining is discontinued.
To be used in the durable fabrics, the fibers making up the fabric have to be, inter alia, stable during dyeing and heat setting processes. For an elastic polyolefin fiber to be stable under dyeing and heat-setting conditions, it must be crosslinked. These fibers can be crosslinked by one or more of a number of different methods, e.g., e-beam or UV irradiation, silane or azide treatment, peroxide, etc., some methods better than others for fibers of a particular composition. For example, polyolefin fibers that are irradiated under an inert atmosphere (as opposed to irradiated under air) tend to be highly stable during dyeing processes (that is, the fibers do not melt or fuse together). The addition of a mixture of hindered phenol and hindered amine stabilizers further stabilized such fibers at heat setting conditions (200-2100 C).
Lycra®, a segmented polyurethane elastic material manufactured by E. I. du Pont de Nemours Company, is currently used in various durable stretch fabrics. Lycra, however, is not stable at the typical high heat-setting temperatures (200-210° C.) used for polyethylene terephthalate (PET) fiber. Moreover, and similar to ordinary uncrosslinked polyolefin-based elastic materials, Lycra fabrics tend to lose their integrity, shape and elastic properties when subjected to elevated service temperatures such as those encountered in washing, drying and ironing. As such, Lycra can not be easily used in co-knitting applications with high temperature fibers such as polyester fibers.